With the open availability of the Global Positioning System (GPS) and other satellite-based positioning systems, personal location tracking devices have gained widespread acceptance and popularity in recent years. By receiving and analyzing satellite signals, such devices can quickly compute their location using well known positioning algorithms and can present the computed location as it changes over time, superimposed on a street map for convenient viewing by a user. Consequently, such a device enables a person to see where they are located as they move from place to place.
Increasingly, vehicles are equipped with built-in navigation units, for instance. Such units enable a driver to readily track where the vehicle is located. Further, provided with mapping data and a destination location entered by the driver, such units can provide the driver with real-time turn-by-turn directions to reach the destination. Portable navigation units with similar functionality are also widely available and can be conveniently mounted in a vehicle or carried by a person to facilitate location tracking and navigation. Unfortunately, however, these navigation units tend to be fairly expensive, thus preventing more widespread market penetration.
Due to government regulations that require cellular wireless carriers to enable determination of cell phone location for emergency response (E-911), virtually all cell phones manufactured and sold today also happen to include a GPS receiver. When a cell phone user calls 911 or another emergency number, the cell phone's location can thus be determined with a fairly high degree of accuracy and reported to a public safety answering point, to facilitate emergency response.
In practice, the cell phone receives from its serving wireless carrier a set of satellite-assistance-data that provides the cell phone with parameters regarding satellites covering the cell phone's current cellular wireless coverage area. The cell phone then uses the assistance-data to tune to various satellites and to receive satellite signals. In turn, the cell phone may use those signals to compute its own location, or the cell phone may send those signals to a location-determination system in the wireless carrier's network, and that system may use the signals to compute the cell phone's location. In either case, the computed location may then be reported to the public safety answering point handing the cell phone's emergency call.
Further, the same technology can be employed to facilitate a myriad of commercial location-based services for cell phone users. For instance, a cell phone user may engage in a wireless-web session with a location-based service provider to learn the location of a store or other establishment nearest to the user's current location, without the need for the user to enter the current location in the form of a street address for instance. The cell phone or network may simply determine the cell phone's location and report that location to the location-based service provider, and the location-based service provider may then use the reported location to look up nearby stores or other establishments. As with the navigation units described above, such technology can also be used to provide cell phone users with travel routing and other useful navigation services.